1. Field of the invention
The present invention relates to a method for reducing the travel time for an optical pick-up and an apparatus thereof by taking into consideration the effect of the rotation of an optical disk on the search process of the optical pick-up so as to more precisely control its tracking.
2. Description of prior art
In prior art, there are two operating modes to access an optical disk, i.e., CLV (constant linear velocity) mode and CAV (constant angular velocity) mode. The CLV mode adjusts the rotation speed of an optical disk according to the location of the pick-up. That is, the rotation speed of the optical disk while the pick-up is at the outer portion of the optical disk is slower than that while the pick-up is at the inner portion of the optical disk. In the CAV mode, on the other hand, the rotation speed of the optical disk is constant, e.g., it is not varied according to the location of the pick-up. It is common to access an optical disk by using both of the CLV mode and the CAV mode in a practical application. The rotation speed to access optical disks is normally several thousands RPM or more.
In the known technologies, travel time is defined as the time required for the optical pickup to move until reaching the desired location of the optical disc. To reduce the travel time, the optical pick-up can move rapidly by a "track jump". The track-jumping signal is used to control the search process of the optical pick-up. However, while the optical disk is rotated at a high speed, the effect of this high-speed rotation on the track-jumping signal has never been addressed. In fact, when the optical disk is rotated at high speed, the track-jumping signal detected by the pick-up controller is not equal to the tracks actually being jumped by the pick-up. Referring to FIG. 1a, in the case that the optical disk is still, track-jumping signals are respectively generated at positions A, B, C, D, E and F. Therefore, six track-jumping signals are generated while the pick-up is moved from A to F, i.e., from the n-th track to the n+5-th track. The arrow in the drawing indicates the direction that the optical disk rotates. Referring to FIG. 1b, in the case that the optical disk is rotated at high speed, track-jumping signals are respectively generated at positions A', B', C', D' and E'. Therefore, only five track-jumping signals are generated while the pick-up is moved from A' to E', i.e., from the n-th track to the n+5-th track. By comparing the results of FIGS. 1a and 1b, it is found that different numbers of track-jumping signals are obtained while the pick-up is jumping the same number of track for the optical disk depending on whether it is still or rotating at high speed. Accordingly, errors will occur when the search process of a pick-up is controlled without considering the effect of high-speed rotation of the optical disk. In order to precisely place the pick-up at the predetermined destination, the controller needs to compensate for such errors by means of subsequent correction. However, this results in a longer travel time for the pick-up.
Referring to FIG. 2, the data recorded on an optical disk is sequentially arranged in a spiral. Even when the pick-up is still, the pick-up controller will continuously detect a track-jumping signal at the position A" if the optical disk is rotated. The number of track-jumping signals being detected in a certain period is equal to the number of revolutions of the optical disk in said period.